Oligomeric bis-phosphates, which are useful as flame retardants in resin compositions such as polycarbonate (PC)/styrenic containing alloys, are typically in the form of viscous liquids and require special equipment for handling during processing, especially in cold climate locations. The viscous liquid phosphates are often pumped into compounding extruders after the thermoplastic polymers, i.e. resins, are melted through heat and mechanical shear. Specialized equipment may include heated reservoirs with heat-traced supply lines designed to keep the oligomeric bis-phosphates fluid so as not to interfere with the extrusion process. Even with the use of specialized equipment, additional steps need to be taken during processing so as to avoid this problem and other problems.
Alternatively, solid phosphate ester flame retardants such as triphenyl phosphate, which is typically available in a flaked form, can be used. However, these solid phosphate ester flame retardants tend to melt prematurely in the feed zone of the extruder causing the composite pre-mixture to “bridge” thereby interfering with the mixing operation.
In view of the foregoing, what is needed are flame retardants for use in resin compositions that have improved physical characteristics and avoid the processing problems described above. Accordingly, the invention herein is directed to oligomeric bis-phosphate flame retardants having desirable physical properties and characteristics which when compounded with resins provide compositions having excellent flame retardancy and improved physical properties, as Compared with previously provided flame retarded resin compositions.